1. Field of the Invention
The present invention relates to an apparatus for and a method of controlling multiple time-varying processes through the use of an adaptive data acquisition scheme, but more specifically, it relates to an adaptive control device wherein a state estimator is used to extrapolate the current state of each controlled process as well as an estimate of the uncertainty of each state.
2. Description of the Prior Art
A process is a "specific, continuous action, operation, of series of changes." More specifically, a process may be the mixing of chemicals to form a compound, the refining of crude oil into its constituents, the movement of a mechanical device, or the maneuvering of a target being tracked by radar, among others. The control of state of each one of the foregoing processes is usually done by a dedicated controller. Many of the processes proceed at rates which are slow relative to the processing capabilities of digital computers which can be used for control. Also, processes may proceed at variable rates which require more detailed attention at some times than at others to ensure the same quality of control.
An alternative to the use of a dedicated controller for each process is to use a centralized controller with distributed control or estimation of the various processes. If the processes are deterministic, well understood, and proceed at constant rates, then the sequencing of measurements of each process for state estimation and control is straightforward. However, if the dynamics of the process, the statistics associated with the noise in the process or noise in the measurements are time variant, other methods of determining the sequence of data acquisition must be employed to ensure adequate and stable control.
Prior art methods of centralized control, as far as is known, are based on fixed sampling rates. These sampling rates are determined by the dynamics of the process, the noise associated with the measurements of the process and the magnitude of the uncertainties about the processes to be controlled. For a given set of conditions, a sampling rate can be chosen which will insure a stable control system. However, if the dynamics or statistic of a process change, the sampling rate may be insufficient or too high. In the first case, this leads to system instability and in the latter case a waste of computer time.
It has been shown in a theoretical study of sequence methods for data acquisition, ("Information Directed Data Acquisition", K. J. Hintz, Doctoral Dissertation, University of Virginia, August 1980), that various criteria can be used for selecting which of several processes to update when multiple processes are to be controlled by a single central processor. Although a specific example of the use for a device implementing these theoretical concepts was presented (ibid., page 2), no specific implementation information was presented. Consequently, there is a need in the prior art to configure a specific implementation of the conceptual ideas presented in the reference document so as to configure an adaptive control device for controlling time varying processes in an improved manner.
An example of the use of the foregoing method might be in the operation of a heat/cool system. The central controller device used in such a system would have many functions to perform but they need not all be performed simultaneously. The central control element can apportion its time dynamically to the various tasks under its control based on their need for central processor interaction. This central processor may control the actions of several distributed processors each assigned a particular task. The amount of time or effort the central processor applies to monitoring each task is based on its uncertainty about the state of that task. It can also be decided how much of its efforts can be devoted to assisting that distributed processor in doing its task.
The prior art, as indicated hereinabove, included advances in adaptive control of processes, including control of time varying processes. However, in so far as can be determined, no prior art adaptive control processing device incorporates all of the features and advantages of the present invention.